Electric vehicles having a motor for running mounted in place of an engine (including vehicles having the motor for running operated by a fuel cell) have been developed and put to practical use. Further, hybrid vehicles having a motor for running mounted in addition to an engine have also been developed and put to practical use. Such a vehicle is provided with a battery for running that outputs driving electric power to the motor for running. The battery for running involves a chemical reaction at the time of charging/discharging and, therefore, it must be cooled to prevent battery degradation caused when the battery attains to a high temperature.
In view of such a problem, Japanese Patent Laying-Open No. 2004-1674 discloses a battery temperature control device that reliably cools an in-vehicle battery. The battery temperature control device is applied to a vehicle having a rear air conditioner unit, which is installed at a rear part of the vehicle and contains air temperature adjusting means for adjusting temperature of the air blown out to the vehicle compartment, and the device controls the temperature of in-vehicle battery. The battery temperature control device has a duct leading the air that has passed through the air temperature adjusting means to the battery, and the air led by the duct is supplied to the battery, whereby the battery temperature is controlled.
According to the laid-open application, by the battery temperature control device, it is possible, when cooling the battery, to lower the air temperature blown to the battery than in the conventional example in which air in the vehicle compartment is blown to the battery.
In the battery temperature control device disclosed in the laid-open application, however, a plurality of routes are formed, including a route for the air in the compartment circulating to the battery and a route for cooling the battery using the air cooled by the air conditioner. As a result, it becomes impossible to accurately grasp the cooling performance of the cooling fan only from information related to the state of operation of the cooling fan (such as a duty command value or fan rotation speed). The reason for this is that pressure loss differs route by route, and that if a plurality of cooling fans are provided on distribution routes of a cooling medium, battery cooling performance varies even when the cooling fans operate in a similar manner. This possibly leads to lower accuracy of cooling control of the battery, or to a delay in determining an abnormality condition such as an excessive charging of the battery.